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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

STMicroelectronics BFX34

Name: BFX34
Brand: STMicroelectronics
SKU: BFX34
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BFX34

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-205AD, TO-39-3 Metal Can

Datasheet:: BFX34.pdf

Description:: TRANS NPN 60V 5A TO-39

Quantity:: RFQ Add To RFQ list

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Inventory:7,713

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Product details

Overview

BFX34 from STMicroelectronics is a silicon epitaxial planar NPN transistor in a TO-39 metal can package, designed for high-current switching and amplification. It delivers 5 A collector current, 60 V V_CEO, 0.4 V typical V_CE(sat) at 5 A/0.5 A drive, 70–100 MHz f_T, and operates up to 200 °C junction temperature-used in relay drivers, inverters, and switching power supplies.

For engineers reviewing the BFX34 datasheet, BFX34 pinout, BFX34 application, or BFX34 equivalent, key selection criteria include saturation voltage at high current, thermal resistance (R_thj-case = 35 °C/W), DC current gain (h_FE ≥ 40 at 1 A), switching speed (t_on/t_off ≤ 0.6/1.2 µs), and rugged TO-39 metal-can construction for industrial power stages.

Technical Context

The BFX34 employs an epitaxial planar structure optimized for low-saturation operation under sustained 5 A collector current. Its high f_T (70–100 MHz) and fast switching (t_on ≤ 0.6 µs, t_off ≤ 1.2 µs) support high-frequency power control in hard-switched topologies.

Rated for 200 °C maximum junction temperature and featuring R_thj-case = 35 °C/W, it enables direct mounting to heatsinks in compact power driver modules without derating at ambient temperatures up to 85 °C.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - supports operation in 48 V bus systems with margin against transients
I_C	5 A continuous - drives high-power relays, solenoids, or MOSFET gate banks directly
V_CE(sat)	0.4 V typ. @ 5 A/0.5 A - minimizes conduction loss (≤ 2 W dissipation at full load)
f_T	70–100 MHz - enables stable linear amplification up to VHF band and fast PWM edge fidelity
R_thj-case	35 °C/W - allows direct heatsink mounting with predictable thermal rise under pulsed or DC loads
h_FE	40–150 - provides wide base drive flexibility across 1–2 A collector currents with stable gain
t_off	0.25–1.2 µs - ensures clean turn-off in 100 kHz-class switching converters without tail current issues

Pinout & Package

TO-39 metal can package: hermetically sealed, center-tab cathode-connected case, axial leads, rated for >200 °C junction operation and mechanical robustness in industrial environments.

Pin/Terminal	Circuit Role	Design Meaning
Emitter (E)	Current sink terminal	Low-impedance return path; internally bonded to case tab in standard orientation
Base (B)	Control input	Receives 0.5 A drive for full 5 A saturation; requires external current-limiting resistor
Collector (C)	High-current output	Connected to case tab in TO-39; must be electrically isolated from heatsink unless referenced to emitter

Key Features

Feature	Design Value
Ultra-low V_CE(sat)	0.4 V typical at 5 A - reduces conduction losses by >40% vs. standard power transistors
High f_T	70–100 MHz - maintains gain and phase margin in broadband amplifier designs
Robust thermal rating	200 °C max T_j - enables operation in enclosed, unventilated enclosures without forced cooling
Fast switching	t_on/t_off ≤ 0.6/1.2 µs - supports >500 kHz PWM in resonant or quasi-resonant topologies
Hermetic TO-39	Metal-can package - provides EMI shielding, moisture immunity, and long-term reliability in harsh environments

Applications

Relay Driver Stage

Inverter Half-Bridge Switch

Use Scenario: Driving 24 V/2 A electromagnetic relays in PLC I/O modules with 100 ms on/off cycling.

IC Role / Device Role / Timing Role: High-current NPN switch sinking relay coil current; base driven by microcontroller GPIO via 1 kΩ resistor.

Use Value: 0.4 V V_CE(sat) limits relay coil power loss to <1 W, eliminating need for auxiliary heat sinking.

Use Scenario: Low-side switch in 48 V solar microinverter half-bridge stage operating at 100 kHz.

IC Role / Device Role / Timing Role: Fast-switching NPN power switch controlling inductive load; paired with freewheeling diode.

Use Value: 0.25–1.2 µs t_off prevents shoot-through during dead-time transitions and reduces switching loss.

Switching Power Supply

DC Motor H-Bridge Driver

Use Scenario: Primary-side switch in 150 W offline flyback converter with 60 V clamp voltage.

IC Role / Device Role / Timing Role: Main power switch handling 5 A peak primary current; driven by UC384X controller.

Use Value: 60 V V_CEO and 200 °C T_j ensure safe operation under reflected surge voltages and high ambient conditions.

Use Scenario: Low-side switch in 24 V brushed DC motor driver for industrial actuator with 3 A stall current.

IC Role / Device Role / Timing Role: Current-sinking transistor in H-bridge leg; base driven by optocoupled logic.

Use Value: 5 A I_C rating and 35 °C/W R_thj-case allow direct heatsink mounting without thermal derating at 40 °C ambient.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN power transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU508A	Higher V_CEO (1000 V), lower f_T (4 MHz), slower switching (t_off ≈ 1.5 µs)	Suitable for line-voltage SMPS but not high-frequency inverters	Select when primary requirement is high-voltage blocking over speed
MJE13009	Lower V_CEO (400 V), higher V_CE(sat) (1.2 V typ.), same TO-220 package	Better for medium-voltage, medium-speed flyback or forward converters	Choose when TO-220 footprint compatibility is required and 0.4 V saturation is not critical

Compared with BU508A and MJE13009, the BFX34 uniquely balances 5 A current, 60 V rating, sub-1 V saturation, and >70 MHz bandwidth in a hermetic TO-39 package-making it optimal for compact, high-reliability 48–60 V industrial switching stages where thermal and EMI constraints apply.

Availability

BFX34 is available at Aetrix Electronics and suitable for relay drivers, switching power supplies, and inverter half-bridge stages requiring stable component supply and long-term industrial availability.

Supply support for BFX34 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The BFX34 belongs to ST's legacy high-reliability power bipolar transistor family, engineered specifically for ruggedized industrial control and power conversion where hermetic packaging and thermal resilience are mandatory.

FAQ

Is the BFX34 pinout compatible with standard TO-39 NPN transistors?

Yes-the BFX34 uses the standard TO-39 pinout: Emitter (lead 1), Base (lead 2), Collector (case/tab). This matches JEDEC TO-39 mechanical specification and is mechanically and electrically interchangeable with other TO-39 NPN devices like the 2N3055 or MJ15003 in layout and mounting, though electrical parameters differ.

Can the BFX34 be used in linear amplifier applications?

Yes-it is specified for linear operation with h_FE = 40–150 at 1–2 A and f_T = 70–100 MHz. Its low V_CE(sat) and high f_T support Class-A/B audio and RF amplifiers up to ~30 MHz, provided adequate heatsinking is applied per its 35 °C/W R_thj-case rating.

What is the maximum safe operating area (SOA) limitation for the BFX34 at 25 °C case temperature?

At T_case = 25 °C, the BFX34's SOA is bounded by 5 A/60 V DC, with pulse limits extending to 10 A for ≤300 µs (1.5% duty cycle). The device enters second breakdown above 2 A × 40 V in linear region; safe operation requires adherence to published SOA curves in ST's AN276 application note.

Does the TO-39 metal case require electrical isolation when mounted to a heatsink?

Yes-the collector is internally connected to the TO-39 case. Mounting directly to a conductive heatsink shorts the collector to ground unless an insulating washer (e.g., mica or silicone pad) and shoulder washer are used. Isolation voltage rating depends on insulator thickness and material; ST recommends ≥2 kV isolation for industrial use.

BFX34 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-205AD, TO-39-3 Metal Can

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 5 A

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 1V @ 500mA, 5A

Current - Collector Cutoff (Max):: 10µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 40 @ 2A, 2V

Power - Max:: 870 mW

Frequency - Transition:: 100MHz

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-39

BFX34 FAQ

1.How can I place an order for BFX34 through Aetrix?

Please submit a Request for Quotation (RFQ) for BFX34 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for BFX34 reliable?

The price and inventory of BFX34 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BFX34 is usually 5 days.

3.What payment methods are accepted for BFX34?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BFX34 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BFX34?

BFX34 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BFX34 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for BFX34?

For technical support, including BFX34 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BFX34 requirements.

6.How does Aetrix verify that BFX34 is sourced from the original manufacturer or authorized distributors?

All BFX34 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that BFX34 meets industry standards.

7.What is the process for return or replacement of BFX34?

All BFX34 units undergo pre-shipment inspection (PSI). If there is an issue with BFX34, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The BFX34 part is unused and in its original packaging.

Return procedure for BFX34:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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